1. Field of the Invention
The present invention relates to battery power management, and more particularly to an integrated battery charger and system regulator circuit that controls battery charging while preventing a system bus node from dropping below a minimum voltage level and to improve the power conversion efficiency.
2. Description of the Related Art
A conventional battery charging power circuit for computing systems or the like, such as laptop or notebook computers, typically regulates battery charging current and battery voltage from an AC adapter. The AC adapter develops DC voltage on a system bus, which is also used to provide input voltage to one or more step-down DC/DC converters. A synchronous buck converter or the like controlled by a battery charger controller uses the system bus voltage as input voltage for developing a voltage used to charge a removable and rechargeable battery. A power source selection device coupled between the battery node and the system bus is turned on to provide power to the system when the AC adapter power source is not available.
A primary drawback for this power architecture is that the DC/DC converters have low power conversion efficiency from the relatively high voltage of system bus. In particular, the output of the AC adapter is between 16 and 20 Volts (V), which is relatively large as compared to the relatively low output voltage of the DC/DC converters, such as on the order of 1.2V or the like, to that the duty cycle of the DC/DC converters must be very small. A potential solution to improve the power conversion efficiency of the step-down DC/DC converters is to connect their inputs directly to the positive battery terminal, which also forms the system bus. A primary issue with this solution is that the voltage of system bus crashes (e.g., drops below a minimum voltage level) for the extremely discharged or bad battery, resulting in system failure.
It is desired to provide a reduced voltage system bus to improve the efficiency of step-down DC/DC converters while also coupling a rechargeable battery without threatening system failure in the event of a discharged or bad battery.